1. Field of the Invention
The present invention relates to a receiver and a receiving method of an Orthogonal Frequency Division Multiplexing (OFDM) system. More particularly, the present invention relates to a receiver and a receiving method of a combinerless Linear amplification with Nonlinear Component (LINC) OFDM system.
2. Descriptions of the Related Art
Orthogonal Frequency Division Multiplexing (OFDM) is a technique that is commonly used in a wireless communication system. One of the main drawbacks of OFDM systems is its high peak to average power ratio, which yields the high power consumption problem.
The linear amplification with nonlinear component (LINC) technique is an effective remedy to the aforementioned drawbacks. A transmitter 1 of a conventional combinerless LINC OFDM system is illustrated in FIG. 1, which comprises a channel encoder 11, an interleaver 12, a symbol mapper 13, an inverse discrete Fourier transformer 14, a signal component separator 15, two cyclic prefix (CP) insertion units 16a, 16b, two power amplifiers 17a, 17b, and two antennas 18a, 18b. 
In the transmitter 1, a bit sequence 100 is processed by the channel encoder 11, the interleaver 12, the symbol mapper 13, and the inverse discrete Fourier transformer 14 in sequence in order to generate an OFDM modulated signal 102. The operations performed by the channel encoder 11, the interleaver 12, the symbol mapper 13, and the inverse discrete Fourier transformer 14 are well-known to people ordinary skilled in the art. Afterwards, the OFDM modulated signal 102 is passed to the signal component separator 15 and then decomposed into two constant-envelope component signals 104a, 104b. Then, the two constant-envelope component signals 104a, 104b are processed by the CP insertion units 16a, 16b and the two high efficiency nonlinear power amplifiers 17a, 17b. Next, the amplified signals 106a, 106b are transmitted by the antennas 18a, 18b, respectively. With the two antennas 18a, 18b, two component signals can be naturally combined at the receiver.
Although conventional combinerless LINC OFDM systems can avoid the drawback of conventional OFDM systems, it yields another problem though. To be more specific, the performance of a receiver of a conventional combinerless LINC-OFDM system will be seriously affected if there is difference, even small, between the channels of the antennas 18a, 18b that the two amplified signals 106a, 106b propagate. Although using a maximum likelihood (ML) detector at the receiver for estimating the bit sequence 100 can effectively solve the problem, its computational complexity is extremely high. Consequently, there is an urgent need in providing a receiving mechanism for combinerless LINC OFDM systems.